Growth of Highly Anisotropic 2D Ternary CaTe₂O₅ Flakes on Molten Glass

Abstract

Two-dimensional (2D) ternary compounds (2DTCs) have attracted intensive attention due to the new degree of freedom of modulating physical and chemical properties. However, the controllable synthesis of 2DTCs still remains a great challenge impeding further research and applications. Here, for the first time, ultrathin (≈7.4 nm) ε-CaTe 2 O 5 flakes with high anisotropy are obtained by a chemical vapor deposition method using soda-lime glass as the capture substrate. The molten glass adsorbs Te vapor in the gas flow to its surface, which reacts with CaO in the molten substrate leading to the precipitation of ε-CaTe 2 O 5 . Interestingly, ε-CaTe 2 O 5 flakes display highly anisotropic band structures and optical properties. Furthermore, low-temperature electrical measurements show that the metal-semiconductor/ insulator transition of ε-CaTe 2 O 5 is exhibited at about 130 K, and optical phonon assisted hopping of small polarons becomes dominant within the temperature range of 130-300 K. Employing soda-lime glass as the capture substrate may provide a new approach for the synthesis of 2DTCs.freedom endows 2DTCs novel physical and chemical properties such as the tunable band gap and variable crystal structure, which may lead to great applications in electronics and optoelectronics. As an important member of 2DTCs, CaTe 2 O 5 has excellent ionic conductivity, [14,15] ferroelastic [16] and optical properties. [17] Owing to the special electronic configuration of tellurium (VI), its electron lone pair will trigger several coordination and unusual structures. Furthermore, the in-plane low symmetric structure may lead to some interesting phenomena such as anisotropic optical and electrical properties. However, there are few reports on 2D CaTe 2 O 5 structures to the best of our knowledge, thus their optical and electrical properties remain unexplored. The synthesis of 2D CaTe 2 O 5 is a huge challenge due to the coexisting hybrid phases in the products such as α, β, γ, ε, δ-phases. [18,19] Thus it is highly desirable to explore an effective way to realize the controllable synthesis of 2D CaTe 2 O 5 structures, which may promote its applications in electronics and optoelectronics.In this work, for the first time, ultrathin (≈7.4 nm) ε-CaTe 2 O 5 flakes are realized by chemical vapor deposition (CVD) method using soda-lime glass as the trapping substrate. The band structure of ε-CaTe 2 O 5 shows different strain-dependence along three directions (a, b, and c axes). The angle-resolved polarized Raman spectra indicate strong in-plane anisotropy in the ε-CaTe 2 O 5 flakes, and the Raman peaks at 124 cm −1 decrease linearly with increasing temperature. Impressively, low-temperature electrical measurements show metal-semiconductor/ insulator transition of ε-CaTe 2 O 5 at about 130 K. These characterizations prove the high anisotropy of ε-CaTe 2 O 5 indicating promising applications in novel electronics and optoelectronics. Results and DiscussionUltrathin, single-crystalline ε-CaTe 2 O 5 flakes were synthesized by CVD method, empl...

Controllable growth of type‐II Dirac semimetal PtTe2 atomic layer on Au substrate for sensitive room temperature terahertz photodetection

“…Because Te can lower the melting point of Au by forming Te-Au eutectic alloy, we can obtain a quasi-atomic smooth and homogeneous molten Au surface, which is considered as an ideal substrate for the epitaxial growth of 2D materials. 39,43,44 Therefore, it is quite promising to develop the controllable synthesis of 2D PtTe 2 crystals on Au substrate, which is essential for their successful application in highspeed photodetection over wide-band wavelength regime benefiting from their gapless nature.…”

Space‐Confined Growth of 2D InI Showing High Sensitivity in Photodetection

“…According to Davis and Mott’s variable‐range hopping model, the conductance curve behavior can be fitted well with it (Equation ()), in contrast with optical phonon‐assisted hopping model, which described the behavior at a higher temperature range where σ 0 and T 0 are defined as the prefactor of conductance and temperature constant, respectively. [ 42,43 ]…”

Synergistic Additive‐Assisted Growth of 2D Ternary In2SnS4 with Giant Gate‐Tunable Polarization‐Sensitive Photoresponse

“…The intensity of the Raman vibration mode is represented by a color scale. It can be seen that the peak centered at 283 cm −1 reaches the maximum at 90° and 270° in horizontal configurations, which corresponds to the direction along the [ 1–30 ] (Figure S5, Supporting Information), and reaches the maximum at 45°, 135°, 225°, and 315° in vertical configurations. The polarization diagrams in Figure 2e,f further clearly show the Raman intensity variation, which can be described as [ 32,34,35 ] where R represents the Raman tensor of In 2 SnS 4 , e i and e s stand for unit polarization vectors of the incident and scattered light, respectively.…”

“…Then Figure 3d shows the absorbance evolution extracted at 650 nm, the data exhibited a two‐lobed shape, which fits well to the sine function, obviously indicating the linear dichroism of In 2 SnS 4 . The absorbance at 650 nm reaches its maximum value at 0° and 180°, which corresponds to the direction along, [ 1–30 ] and reaches its minimum value at 90° and 270°, which corresponds to the direction parallel to the c ‐axis (Figure S5, Supporting Information). It confirms that the dominate direction of polar absorption is perpendicular to the c ‐axis.…”

“…The incident laser with different polarization directions encounters a varying absorption when it travels across the In 2 SnS 4 channel, reflecting the intrinsically dichroic ratio (≈1.46) of the In 2 SnS 4 crystals. Based on HAADF characterizations and the crystal structure, we labelled the axis of the crystal and defined it as x‐axis (along [ 1–30 ] ) and y ‐axis ( y ‐axis corresponds to the c‐axis of the In 2 SnS 4 crystal). Then we extracted the transfer characteristic curve at source‐drain voltage V ds = 3 V along x direction and y direction, and calculated the dichroic ratio as a function of the gate voltage, as shown in Figure 5c.…”